What Causes Delay In Menstruation Other Than Pregnancy?

Hi I'm 32 years old, my last menstrual cycle started 30/08/2010 and ended 4/09/2010. on the 30/09/2010 i had a discharge of blood and mucus and then 2 days of peach spotting (no panty liner needed only after wiping). my cycle has not started and i have taken a home pregnancy test 10/10/10 which was negative. I have had no symptoms accept a little nausea randomly through out the day